Spread spectrum transmission systems

ABSTRACT

A code phase signalling module arranged to provide code phase signalling to assist in signal acquisition of direct sequence spread spectrum signalling received by a receiver module from a transmitter module. The code phase signalling is arranged to be used by the receiver module to synchronise the phase of a synchronisation code provided from within the receiver module with the phase of a modulation code of the direct spread spectrum sequence signalling received by the receiver module. The synchronisation code sequence corresponds to the modulation code sequence. The code phase signalling module is arranged to provide code phase time signalling representing the offset time of the synchronisation code from a reference time. The reference time is associated with the time of transmission of a particular reference portion of the modulation code of the direct spread spectrum signaling.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the field of Spread SpectrumTransmission Systems, specifically Direct Sequence Spread Spectrumtransmission as employed in CDMA (code division multiple access)transmission systems. It is particularly relevant to satellitenavigation systems, such as the GPS (Global Positioning System), theGlonass system (the Russian satellite navigation system) and the Galileosystem (the European satellite navigation system currently underdevelopment) which employ CDMA transmission.

BACKGROUND TO THE INVENTION

There are three types of Spread Spectrum Transmission System. These are:

-   1. Frequency hopping—the signal is rapidly switched between    different frequencies within the hopping bandwidth pseudo-randomly,    and the receiver knows before hand where to find the signal at any    given time.-   2. Time hopping—the signal is transmitted in short bursts    pseudo-randomly, and the receiver knows beforehand when to expect    the burst.-   3. Direct sequence—the digital data is directly coded at a much    higher frequency. The code is generated pseudo-randomly, the    receiver knows how to generate the same code, and correlates the    received signal with that code to extract the data.

In general, such Spread Spectrum transmission systems are distinguishedby three key elements:

-   i) The signal occupies a bandwidth much greater than that which is    necessary to send the information. This results in many benefits,    such as immunity to interference and jamming and multi-user access.-   ii) The bandwidth is spread by means of a code which is independent    of the data. The independence of the code distinguishes this from    standard modulation schemes in which the data modulation will always    spread the spectrum somewhat.-   iii) The receiver synchronizes to the code to recover the data. The    use of an independent code and synchronous reception allows multiple    users to access the same frequency band at the same time.

In order to protect the signal, the code used is pseudo-random. Itappears random, but is actually deterministic, so that the receiver canreconstruct the code for synchronous detection. This pseudo-random codeis also called pseudo-noise (PN).

The present invention is particularly relevant to CDMA transmission,which is a form of Direct Sequence Spread Spectrum transmission. CDMAcan be used for the transmission of digitized voice, ISDN channels,modem data, etc. Such transmission is shown in FIG. 1, which shows asimplified Direct Sequence Spread Spectrum CDMA system. For clarity, thefigure shows one channel operating in one direction only. FIG. 2illustrates how information data modulates the pseudorandom code. Thegeneral operating principles of such a CDMA system are well known andwill not be considered in detail here. However, it can be considered tocomprise the following in which:

-   A) Signal transmission consists of the following steps (FIG. 1, FIG.    2):    -   1. A pseudo-random code is generated, different for each channel        and each successive connection.    -   2. The Information “signal” data modulates the pseudo-random        code (the Information data is “spread”, FIG. 2).    -   3. The resulting signal modulates a carrier.    -   4. The modulated carrier is amplified and broadcast.-   B) Signal reception consists of the following steps (FIG. 1):    -   1. The carrier is received and amplified.    -   2. The received signal is mixed with a local carrier to recover        the spread digital signal.    -   3. A pseudo-random code is generated, matching the anticipated        signal.    -   4. The receiver acquires the received code and phase locks its        own code to it.    -   5. The received signal is correlated with the generated code,        extracting the Information data.

Satellite navigation systems, such as GPS and Galileo, use a CDMAtransmission system. For simplicity, the foregoing text will focus onsatellite navigation systems, taking the GPS system as a specificexample.

The GPS system presently comprises more than 24 satellites, of whichusually from 8 to 16 are simultaneously within the sight of a receiver.These satellites transmit e.g. orbital parameters, time information ofthe transmission, etc. A receiver, used in positioning, normally deducesits position by calculating the propagation time of a signal transmittedsimultaneously from several satellites, belonging to the positioningsystem, to the receiver. For the positioning, the receiver musttypically receive the signal of at least four satellites within sight tocompute the position.

Each satellite of the GPS system transmits a “ranging” signal at acarrier frequency of 1575.42 MHz called L1. This frequency is alsoindicated with 154f0, where f0=10.23 MHz. Furthermore, the satellitestransmit another “ranging” signal at a carrier frequency of 1227.6 MHzcalled L2, i.e. 120f0. However, this L2 signal is not in civilian useand will not be described in detail here.

In the satellite, the modulation of these signals is performed with atleast one pseudo random sequence. This pseudo random sequence isdifferent for each satellite and each “ranging” signal from eachsatellite. As a result of the modulation, a code-modulated wideband“ranging” signal is generated. The modulation technique used makes itpossible in the receiver to distinguish between the signals transmittedfrom different satellites, although the carrier frequencies used in thetransmission are substantially the same (i.e. CDMA).

In each satellite, for modulating the L1 signal, the pseudo randomsequence used is e.g. a so-called C/A code (Coarse/Acquisition code),which is a code from the family of the Gold codes. Each GPS satellitetransmits a signal by using an individual (unique) C/A code. The codesare formed as a modulo-2 sum of two 1023-bit binary sequences. The firstbinary sequence G1 is formed with a polynome X<10>+X<3>+1, and thesecond binary sequence G2 is formed by delaying the polynomeX<10>+X<9>+X<8>+X<6>+X<3>+X<2>+1 in such a way that the delay isdifferent for each satellite. This arrangement makes it possible toproduce different C/A codes with an identical code generator. The C/Acodes are thus binary codes whose chipping rate in the GPS system is1.023 MHz.

The C/A code comprises 1023 chips, wherein the iteration time (epoch) ofthe code is 1 ms. The carrier of the L1 signal is further modulated bynavigation information at a bit rate of 50 bit/s. The navigationinformation comprises information about the satellite integrity(“health”), orbital parameters, GPS time information, etc.

The satellites are each arranged to transmit the beginning of their C/Acode at the same instant in time, e.g. the start of the week. Once theC/A code from each satellite has been transmitted, the C/A code isrepeated.

During their operation, the satellites monitor the condition of theirequipment. The satellites may use, for example, so-called “watch-dog”operations to detect and report possible faults in the equipment. Theerrors and malfunctions can be instantaneous or longer lasting. On thebasis of the health data, some of the faults can possibly be compensatedfor, or the information transmitted by a malfunctioning satellite can betotally disregarded. Furthermore, in a situation in which the signal ofmore than four satellites can be received, the information received fromdifferent satellites can be weighted differently on the basis of, forinstance, carrier to noise ratio. Thus, it is possible to minimize theeffect of errors on measurements, possibly caused by satellites whichhave a low signal level.

To detect the signals of the satellites and to identify the satellites,the receiver must perform acquisition, whereby the receiver searches forthe signal of each satellite at a time and attempts to be synchronizedand locked to this signal so that the pseudorange measurement (distanceto a satellite) can be made. If the signal level is very low, and thesignal cannot be demodulated it is still possible to make a pseudorangemeasurement, and calculate the receiver position with it if theephemeris information is available

Acquisition of a GPS signal occurs by sequentially adjusting therelative timing, which is defined as code phase, of the stored replica(synchronisation) code sequence in the GPS receiver relative to thereceived signal broadcast by the satellite, and observing thecorrelation output. The alignment of the code phase must be within lessthan one chip of the sequence for any measurable response. This mightmean searching for a response by trying up to all 1,023 possible codephase positions. However, network assistance may speed up this process(see below).

The positioning receiver must perform the acquisition e.g. when thereceiver is turned on and also in a situation in which the receiver hasnot been capable of receiving the signal of any satellite for a longtime. Such a situation can easily occur e.g. in portable devices,because the device is moving and the antenna of the device is not alwaysin an optimal position in relation to the satellites, which impairs thestrength of the signal coming in the receiver. Also, in urban areas,buildings affect the signal to be received, and furthermore, so-calledmultipath propagation can occur, wherein the transmitted signal comesinto the receiver along different paths, e.g. directly from thesatellite (line-of-sight) and also reflected from buildings. Thismultipath propagation causes that the same signal is received as severalsignals with different phases.

Following signal acquisition (and Doppler frequency adjustment to takeaccount of the relative movement between the satellites and thereceiver—not discussed here), the positioning arrangement in thereceiver has two primary functions:

-   1. To calculate the pseudorange between the receiver and the    different GPS satellites, and-   2. To determine the position of the receiver by utilizing the    calculated pseudoranges and the position data of the satellites. The    position data of the satellites at each time can be calculated on    the basis of the Ephemeris received from the satellites.

The distances to the satellites are called pseudoranges, because thetime is not accurately known in the receiver. Thus, the determinationsof position and time are repeated until a sufficient accuracy isachieved with respect to time and position. Because time is not knownwith absolute precision, the position and the time must be determinede.g. by linearizing a set of equations for each new iteration. Thepseudorange can be calculated by measuring the pseudo transmission timedelays between signals of different satellites.

Almost all known GPS receivers utilize correlation methods foracquisition to the code as well as for tracking. In a positioningreceiver, reference synchronisation codes ref(k), i.e. the pseudorandomsequences for different satellites are stored or generated locally. Areceived signal is subjected to conversion to an intermediate frequency(down conversion), after which the receiver multiplies the receivedsignal with the stored pseudo random sequence. The signal obtained as aresult of the multiplication is integrated or low-pass filtered, whereinthe result is data about whether the received signal contained a signaltransmitted by a particular satellite.

The multiplication is iterated in the receiver so that each time, thephase of the (synchronisation) pseudorandom sequence stored in thereceiver is shifted. The correct phase is inferred from the correlationresult, preferably so that when the correlation result is the greatest,the correct phase has been found. Thus, the receiver is correctlysynchronized with the received signal. After the code acquisition hasbeen completed, the next steps are frequency tuning and phase locking.

The above-mentioned acquisition and frequency control process must beperformed for each signal of a satellite received in the receiver. Somereceivers may have several receiving channels, wherein an attempt ismade on each receiving channel to be synchronized with the signal of onesatellite at a time and to find out the information transmitted by thissatellite.

The positioning receiver receives information transmitted by satellitesand performs positioning on the basis of the received information. Forthe positioning, the receiver must receive the signal transmitted by atleast four different satellites to find out the x, y, z coordinates andthe time data. The received navigation information is stored in amemory, wherein this stored information can be used to find out e.g. theEphemeris data of satellites.

As previously mentioned, networks (for example cellular networks whichcan employ GSM, PDC, CDMA, WCDMA, CDMA2000 etc. transmission technology)are known to assist receivers in acquiring the signalling from one ormore satellites to speed up the acquisition process. Thus, rather thanstarting the synchronisation process at an arbitrary bit position in the(synchronisation) pseudorandom code sequence, the starting point forsynchronization, between the received signal and the stored/generated(synchronisation) pseudorandom code sequence is based on informationprovided by the network.

Currently, networks assist the positioning receivers in the code phasesearch by providing the position within a (synchronisation)generated/stored code to be used as a starting position in thecorrelation process with reference to sequence length. Thus, forexample, the network provides that the starting position in thesynchronisation code should be at a position corresponding to position659 from the start of a code sequence.

The starting point is only valid at a certain time, and this validitytime is also provided with the network assistance transmission. Also,the network must somehow provide (or trust that the receiver alreadyhas) knowledge of time into the receiver. However, such time transfermethods are not themselves the focus of the present invention, althoughthey could be used in conduction with the present invention. Afterhaving the knowledge of the code phase starting point at some point intime and knowledge of the current time, the receiver can calculate thecode phase starting point for the current time.

An uncertainty tolerance window is also provided. This is also providedin relation to sequence length. Thus, the starting position may beposition 659+/−8 chip lengths in the code sequence. The uncertaintytolerance window is relevant to the elevation angle of the satellite.This is due to the fact that usually from the acquisition assistanceprovider's perspective the uncertainty of the remote receiver's locationis greater than the uncertainty of the altitude. Therefore, theuncertainty window for the acquisition assistance is greater for thosesatellites, which are low on horizon.

The GPS system uses a pseudorandom code of a fixed length (1023 chips)i.e. each satellite transmitter modulates its signal by a uniquepseudorandom code of the same length. The Galileo system may use avariable length pseudorandom code or it may use a static length code,but the actual length of the code may be different from GPS.

SUMMARY OF THE PRESENT INVENTION

In a first aspect, the present invention provides a code phasesignalling module arranged to provide code phase signalling to assist insignal acquisition of direct sequence spread spectrum signallingreceived by a receiver module from a transmitter module,

-   -   wherein the code phase signalling is arranged to be used by the        receiver module to synchronise the phase of a synchronisation        code provided from within the receiver module with the phase of        a modulation code of the direct spread spectrum sequence        signalling received by the receiver module, the synchronisation        code sequence corresponding to the modulation code sequence,    -   wherein the code phase signalling module is arranged to provide        code phase time signalling representing the offset time of the        synchronisation code from a reference time, wherein the        reference time is associated with the time of transmission of a        particular reference portion of the modulation code of the        direct spread spectrum signalling, and wherein the offset time        is associated with the time of transmission of a subsequently        transmitted offset portion of the modulation code of the direct        spread spectrum sequence signalling.

The code phase signalling provided by the device is independent of thecode length. It is directly based on time and therefore can workregardless of the length of the code.

The module may be arranged to provide code phase signalling in one ormore multi code length direct sequence spread spectrum systems.

The code phase may be used to synchronise with a past, present, orfuture received portion of the code sequence received from thetransmitter module.

The offset time may be used to synchronise with a past, present, orfuture received portion of the code sequence received from transmittermodule.

The modulation code sequence may have a length comprising apredetermined number of chips, and the module may be arranged torepresent the offset time of the modulation code by dividing the numberof chips from the offset position to the reference position by thepredetermined number of chips corresponding to the sequence length.

The modulation code sequence may have a length comprising apredetermined number of chips transmitted at a particular transmissionrate, and the module may be arranged to represent the offset time of themodulation code by dividing the number of from the offset position tothe reference position by the transmission rate of the predeterminednumber of chips corresponding to the sequence length.

The transmitter module may be inside the same device as the receivermodule. The transmitter module may be a PE and the receiver module maybe a ME.

The modulation code may be arranged to cyclically repeat.

The reference time may represent the beginning of a cyclically repeatingmodulation code.

The reference portion may be the beginning, middle or end of the code.

The synchronisation code sequence may be a pseudorandom code sequence.

The synchronisation code sequence may be provided from within thereceiver module by a shift register or a memory.

The direct sequence spread spectrum may be code division multiple accesssignalling.

The module may be comprised in a cellular network device.

The module may be comprised in a receiver comprising the receivermodule.

The module may be comprised in a receiver comprising the receivermodule, and the receiver may be a cellular telecommunications device.

The receiver module may be comprised in a global navigation satellitereceiver.

The receiver module may be a receiver module remote of the module.

The transmitter module may be a transmitter module remote of the module.

The present invention also provides a cellular network device comprisinga module.

The module may be arranged to transmit the code phase signalling via acellular air interface to a receiver module comprised in a cellulartelecommunications device.

In a second aspect, the present invention provides a receiver modulearranged to receive code phase signalling assistance, from a code phasesignalling module, to assist in signal acquisition of direct sequencespread spectrum signalling received by the receiver module from atransmitter module,

-   -   wherein the code phase signalling is arranged to be used by the        receiver module to synchronise the phase of a synchronisation        code provided from within the receiver module with the phase of        a modulation code of the direct spread spectrum sequence        signalling received by the receiver module, the synchronisation        code sequence corresponding to the modulation code sequence,    -   wherein the receiver module is arranged to receive code phase        signalling representing the offset time of the synchronisation        code from a reference time, wherein the reference time is        associated with the time of transmission of a particular        reference portion of the modulation code of the direct spread        spectrum signalling, and wherein the offset time is associated        with the time of transmission of a subsequently transmitted        offset portion of the modulation code of the direct spread        spectrum sequence signalling.

The present invention also comprises computer code arranged to providecode phase signalling assistance and computer code arranged to receivecode phase signalling assistance.

The present invention also encompasses a system comprising a moduleaccording to the first aspect of the invention and a receiver moduleaccording to second aspect of the invention.

The present invention also encompasses a global navigation satellitesystem comprising a module according to the first aspect of theinvention and a receiver module according to second aspect of theinvention.

The present invention encompasses one or more aspects and or embodimentsin appropriately modified one or more combinations. Thus, featuresspecifically recited for one aspect or embodiment of the invention mayalso be provided in another aspect or embodiment of the invention, withappropriate amendments made, even though the specific combination maynot be specifically recited. One or more features of the described priorart may be added to one or more aspects or embodiments of the presentinvention.

BRIEF DESCRIPTION OF THE FIGURES

Specific embodiments of the present invention will now be described withreference to the following Figures in which:

FIG. 1 is an illustration of a Direct Sequence Spread Spectrum System,according to the prior art but applicable to the present invention;

FIG. 2 illustrates Pseudorandom Noise Spreading, according to the priorart, but applicable to the present invention;

FIG. 3 is a schematic illustration of network assistance in a specificembodiment of the present invention;

FIG. 4 is a diagram illustrating a module for providing code phasesignaling; and

FIG. 5 is a diagram illustrating a module for receiving signaling; and

FIG. 6 is a diagram illustrating components of the receiver shown inFIG. 3.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Consider a number of satellite navigation transmitters 1, 2, 3, 4 etc,each continuously modulating their signalling for transmission by acorresponding unique pseudorandom code sequence, P1, P2, P3, P4 . . .etc to provide CDMA signalling. Each satellite is arranged to commencetransmission of its signalling from a reference time, say Monday 12.00am GMT. The commencement of signalling is associated with the beginningof the modulation sequence. Thus, 12.00 am GMT is associated with thebeginning of each of the code sequences P1, P2, P3 and P4. Satellites 1and 4 are associated with GPS GNSS and satellites 2 and 3 are associatedwith the Galileo GNSS. In the present example, the beginning of themodulation sequence for the two systems is the same, i.e. Monday 12 amGMT. However, the beginning of the modulation sequence of the twosystems could start at different times.

Some of the codes have a different sequence length to others. So, forexample, P1 is 1023 chips long, P2 is 4095 (larger than P1) chips long,P3 is 511 (smaller than P1) chips long and P4 is 1023 chips long. Eachsatellite continues with the modulation from the start of the sequenceonce it has come to the end of the sequence. In the case of P1 and P4,this is after every 1 ms. In the case of P2 or P3, it could be anyvalue, for example, 2 ms, 4 ms or 1 ms. For ease of understanding wewill assume it is 1 ms in the present case.

A receiver 100, on the Earth, comprises a cellular (GSM) engine 200,GNSS RF module 101, a GNSS Measurement Engine (ME) module 120 and a GNSSPositioning Engine (PE) module 110. The GNSS RF module 101 is forreception of CDMA GNSS signalling from satellite navigation transmitters1, 2, 3, 4 . . . etc. These signals are provided to the ME 120. The PE110 and ME 120 may be housed in the same Baseband BB box (as shown inFIG. 3) or in different boxes.

The ME 120 is arranged to perform measurements on GNSS signals andconvert them into suitable format for position information calculationin the PE 110. The ME hardware (HW) comprises BB HW module and GNSS RFfront-end HW module (typical GNSS receiver HW), memory for GNSS signalsamples and a processor for processing the sampled and stored GNSSsignals, or a combination of the above.

The ME 120 has necessary low-level software (SW) and logic for carryingout signal acquisition, tracking, validation and data reception. The ME120 also has necessary low-level SW for controlling the GNSS HWaccording to the configuration parameters given from PE 110 (power-save,frequency calibration, time calibration, Automatic Gain Control tuning,measurement interval, etc). The ME 120 can measure signalling from GPS,Glonass, and Galileo satellites, or any combination of these or otherGNSS systems not specifically mentioned here. The term “low-level”relates to any aspect that relates to the real-time acquisition andtracking of satellite signals by the measurement component.

The PE 110 carries out position information calculation (position,velocity, time). The PE 110 produces low-level information for ME 120 toacquire GPS, Glonass and/or Galileo signals, that is, expected signalcode phases, expected Doppler frequency, code and Doppler uncertainties,details of reference frequency, details of reference time. The PE 110produces low-level control for ME 120 to enable power-save, power-offand power-on, self-testing etc. The PE 110 converts the GNSS assistanceinformation from cellular networks or from other sources (WLAN, memory)into suitable format for the ME 120. In other words, PE removes thedependencies (e.g.to cellular network specific things like timetransfer) to assistance data protocols and converts the assistance datainto “GNSS format”.

The PE 110 generates the necessary response messages according to thesupported protocol. The PE 110 can use measurements other than GNSSmeasurements in position information calculation.

The receiver 100 receives the satellite CDMA signalling over the airinterface. It also receives cellular network assistance from a cellularnetwork 300 via e.g. GSM signalling over the air interface. The receiver100 has two antennae and associated HW/SW 101, 200, one to receive CDMAsignalling via the GNSS RF 101 and one to receive the GSM signalling 200(FIG. 3). However, one common antenna could also be used.

The receiver 100 first needs to acquire the signalling from satellites1, 2, 3 and 4 in order to determine its position on the Earth.Acquisition assistance is provided by the network 300.

The receiver 100 knows that satellites 1-4 should be visible. Thisinformation is provided in the receiver memory (not shown), e.g. fromthe last time the receiver 100 was turned on. Also provided in thememory are the pseudorandom codes (e.g. P1-P4) that are used byrespective satellites to modulate their transmissions. These codes areused as synchronisation codes against the received signalling. A highcorrelation between a synchronisation code and the received signallingindicates that the phases of the codes have been matched.

The receiver 100 identifies code P1 from memory 110 (see FIG. 6) inorder to begin the phase synchronisation process with satellite 1. Thestarting position within the code sequence P1 is determined fromacquisition data provided by the cellular network 300.

The present invention can be used in two different interfaces; betweenthe network 300 and receiver 100, and inside the receiver 100 between PE120 and ME 110. So, let's consider the former interface first.

A device inside the network 300 measures the GNSS signals to providecode phase information. (In other embodiments, the device doesn'tnecessarily have to measure the signals but can virtually calculate themusing commonly known techniques.) These GNSS signals (e.g. GPS and/orGalileo) are basically code phase values (and uncertainties), which arethen transformed to seconds by basically dividing the code phase valuewith code length value of the particular system. So, in the case thecode phase length value is 1023 chips/ms (P1), the code phase isrepresented by dividing the code phase value by 1023 chips/ms. In thecase when the code length is 4095 chips/ms (P2), the code phase isrepresented by dividing the code phase value by 4095 chips/ms.

This code phase value can be considered to be a value in seconds, andrepresents the current phase with reference to a reference time, thereference time designating a particular specific position in the codesequence, for example, the beginning/middle/end of the code sequence. Inthe case that the reference time represents the beginning of the codesequence, the code phase value in seconds could represent the timeelapsed from the reference time, the reference time corresponding to thecommencement of signalling from the GNSS transmitters (i.e. offset fromMonday 12 am GMT). However, the code phase value could represent thetime elapsed from the beginning of a particular code sequence which isoffset from the commencement of signalling e.g. the time offset from thebeginning of the 3000^(th) repetition of the code sequence. In thelatter case, fewer bits would be required to represent the value inseconds as the time offset would be comparatively small to thepreviously mentioned example.

The reference time would have to be known by the receiver 100. Thiscould be provided and updated via the network or the GNSS.

This value in seconds, and the signal system identity information (ashort constant value that tells whether the signal is GPS, Galileo, orsomething else) is then transmitted over some carrier to the receiver100. The receiver 100 then uses this information in conjunction with thereference time in the acquisition of satellite signalling.

Consider the example when the reference time is based on Monday 12 amGMT so that the code phase values represent the offset time from Monday12 am GMT. Consider that the current position of the code is 500 chipsfrom Monday 12 am GMT for code sequence P1 and 700 chips from Monday 12am GMT for code sequence P2. The code phase provided by the network tothe receiver 100 is 500/1023 milliseconds for code sequence P1 and700/4095 milliseconds for code sequence P2.

In the case of P1, the receiver 100 receives the code phase 500/1023milliseconds. From the system identity information, the receiver knowsthat this code phase is for GPS signalling. Given that the receiver 100knows the position of the code which corresponds to the reference time,and now it knows that the code phase is 500/1023, it can determine agood approximate to code phase which should be used to begin thecorrelation process for P1.

The same is for P2. The receiver 100 receives the code phase 700/4095milliseconds. From the system identity information, the receiver knowsthat this code phase is for Galileo signalling. Given that the receiver100 knows the position of the code which corresponds to the referencetime, and now it knows that the code phase is 700/4095, it can determinea good approximate to code phase which should be used to begin thecorrelation process for P2.

Of course, there is also a need to transmit the “base time” when thatacquisition assistance was valid. Outside this base time, newacquisition assistance data would be required.

The second interface works exactly the same way, but in that case the PE110 calculates this “value in seconds” either from the acquisitionassistance received from the network or from satellite orbitinformation. This “value in seconds”, signal system identityinformation, uncertainty values (in seconds), and base time is thentransmitted over some carrier (this can be for instance serial port) tothe ME 120, which is basically a DSP processor 120 (see FIG. 6) thatcontrols the actual hardware and then utilizes this information insearch of the satellites.

Reference time for this case is also necessary to send with the “valuein seconds”. In this case, the reference time can be for instance insome form of local time between the PE 110 and the ME 120. A local timecan be for instance some counter value from the baseband or it could beany common reference time.

Generally speaking, the receiver 100 is continuously receivingsignalling from the satellites. The code phase may be used tosynchronise with a past, present or future received portion of the codesequence received from satellites 1, 2, 3, 4 etc. The receiver 100 isarranged to be provided with the appropriate knowledge (over one of theair interfaces or pre-stored) to determine whether synchronisationshould be conducted with a past, current or future received portion ofthe code sequence.

When the receiver is searching for the first satellite, it has to addits own uncertainties (reference time uncertainty, reference frequencyuncertainty, etc) to the uncertainties given in the acquisitionassistance. Once a first satellite is acquired, e.g. 1, the secondsatellite, e.g. 2, can be searched with smaller uncertainty, because nowthe receiver is able to reduce its own uncertainties based on theacquired signal.

Aspects of Doppler shift adjustment conducted in signal acquisition arenot specifically discussed but may be conducted. Furthermore, althoughthe GSM network is specifically mentioned for providing networkassistance, network assistance may be provided via a Wireless Local AreaNetwork (WLAN) transmission system, or any other suitable transmissionsystem.

1. A module for providing code phase time signalling, the module forproviding code phase time signalling comprising at least one processorand at least one memory comprising computer code, the at least onememory and the computer program code configured to, with the at leastone processor, cause the module for providing code phase time signallingto: provide, to an output, code phase time signalling representing anoffset time of a synchronisation code from a reference time, wherein:the code phase time signalling is configured to be used by a module forreceiving signalling to synchronise the phase of a synchronisation codeprovided from within the module for receiving signalling with the phaseof a modulation code of direct sequence spread spectrum signallingreceived by the module for receiving signalling, a sequence of thesynchronisation code corresponding to a sequence of the modulation code;the reference time is associated with the time of transmission of aparticular reference portion of a modulation code of the direct sequencespread spectrum signalling; and the offset time is associated with thetime of transmission of a subsequently transmitted offset portion of themodulation code of the direct sequence spread spectrum signalling.
 2. Amodule for providing code phase time signalling according to claim 1,wherein the module for providing code phase time signalling is a modulefor providing multi code length code phase time signalling configured toprovide code phase time signalling in one or more multi code lengthdirect sequence spread spectrum systems.
 3. A module for providing codephase time signalling according to claim 1, wherein the offset time isused to synchronise with a past, present, or future received portion ofthe modulation code sequence of the direct sequence spread spectrumsignalling, the direct sequence spread spectrum signalling beingreceived from a module for transmitting signalling.
 4. A module forproviding code phase time signalling according to claim 1, wherein themodulation code sequence has a length comprising a predetermined numberof chips, and wherein the module for providing code phase timesignalling is configured to represent the offset time of the modulationcode by dividing the number of chips from the offset position to thereference position by the predetermined number of chips corresponding tothe sequence length.
 5. A module for providing code phase timesignalling according to claim 1, wherein the modulation code sequencehas a length comprising a predetermined number of chips transmitted at aparticular transmission rate, and wherein the module for providing codephase time signalling is configured to represent the offset time of themodulation code by dividing the number of chips from the offset positionto the reference position by the transmission rate of the predeterminednumber of chips corresponding to the sequence length.
 6. A module forproviding code phase time signalling according to claim 1, wherein thedirect sequence spread spectrum signalling is received from a module fortransmitting signalling, the module transmitting signalling being insidethe same device as the module for receiving signalling.
 7. A module forproviding code phase time signalling according to claim 6, wherein themodule for transmitting signalling is a PE (Positioning Engine) and themodule for receiving signalling is a ME (Measurement Engine).
 8. Amodule for providing code phase time signalling according to claim 1,wherein the modulation code is configured to cyclically repeat.
 9. Amodule for providing code phase time signalling according to claim 1,wherein the reference time represents the beginning of a cyclicallyrepeating modulation code.
 10. A module for providing code phase timesignalling according to claim 1, wherein the reference portion is thebeginning, middle or end of the modulation code.
 11. A module forproviding code phase time signalling according to claim 1, wherein thesynchronisation code sequence is a pseudorandom code sequence.
 12. Amodule for providing code phase time signalling according to claim 1,wherein the synchronisation code sequence is provided from within themodule for receiving signalling by a shift register or a memory.
 13. Amodule for providing code phase time signalling according to claim 1,wherein the direct sequence spread spectrum signalling is code divisionmultiple access signalling.
 14. A module for providing code phase timesignalling according to claim 1, wherein the module for providing codephase time signalling is comprised in a cellular network device.
 15. Amodule for providing code phase time signalling according to claim 1,wherein the module for providing code phase time signalling is comprisedin a receiver comprising the module for receiving signalling.
 16. Amodule for providing code phase time signalling according to claim 1,wherein the module for providing code phase time signalling is comprisedin a receiver comprising the module for receiving signalling, andwherein the receiver is a cellular telecommunications device.
 17. Amodule for providing code phase time signalling according to claim 1,wherein the module for receiving signalling is comprised in a globalnavigation satellite receiver.
 18. A module for providing code phasetime signalling according to claim 1, wherein the module for receivingsignalling is a receiver module remote of the module for providing codephase time signalling.
 19. A module for providing code phase timesignalling according to claim 1, wherein the direct sequence spreadspectrum signalling is received from a module for transmittingsignalling, wherein the module for transmitting signalling is atransmitter module remote of the module for providing code phase timesignalling.
 20. A cellular network device comprising a module forproviding code phase time signalling according to claim
 1. 21. A modulefor providing code phase time signalling according to claim 1, whereinthe module is configured to transmit the code phase time signalling viaa cellular air interface to a receiver module comprised in a cellulartelecommunications device.
 22. A module for receiving signalling,comprising at least one processor and at least one memory comprisingcomputer code, the at least one memory and the computer program codeconfigured to, with the at least one processor, cause the module forreceiving signalling to: receive code phase time signalling by an input,the code phase time signalling representing an offset time of asynchronisation code from a reference time, wherein; the reference timeis associated with the time of transmission of a particular referenceportion of a modulation code of received direct sequence spread spectrumsignalling, and the offset time is associated with the time oftransmission of a subsequently transmitted portion of the modulationcode of the direct sequence spread spectrum signalling, and wherein asequence of the synchronisation code corresponds to a sequence of themodulation code; and use the code phase time signalling to synchronisethe phase of a synchronisation code provided from within the module forreceiving signalling with the phase of the modulation code of the directsequence spread spectrum signalling received by the module for receivingsignalling, to assist in signal acquisition of direct sequence spreadspectrum signalling received by the module for receiving signalling. 23.A global navigation system comprising a module for providing code phasetime signalling according to claim 1, and further comprising a modulefor receiving signalling comprising at least one processor and at leastone memory comprising computer code, the at least one memory and thecomputer program code configured to, with the at least one processor,cause the module for receiving signalling to: receive code phase timesignalling by an input, the code phase time signalling representing anoffset time of a synchronisation code from a reference time, wherein:the reference time is associated with the time of transmission of aparticular reference portion of a modulation code of received directsequence spread spectrum signalling, and the offset time is associatedwith the time of transmission of a subsequently transmitted portion ofthe modulation code of the direct sequence spread spectrum signalling,and wherein a sequence of the synchronisation code corresponds to asequence of the modulation code; and use the code phase time signallingto synchronise the phase of a synchronisation code provided from withinthe module for receiving signalling with the phase of the modulationcode of the direct sequence spread spectrum signalling received by themodule for receiving signalling, to assist in signal acquisition ofdirect sequence spread spectrum signalling received by the module forreceiving signalling.
 24. A global navigation satellite systemcomprising a module for providing code phase time signalling accordingto claim
 1. 25. A global navigation satellite system comprising a moduleaccording to claim
 22. 26. A method of providing code phase timesignalling, using at least one processor and at least one memorycomprising computer code, the at least one memory and the computerprogram code configured to, with the at least one processor, perform:providing code phase time signalling representing an offset time of asynchronisation code from a reference time wherein: the code phase timesignalling is configured to be used by a module for receiving signallingto synchronise the phase of a synchronisation code provided from withinthe module for receiving signalling with the phase of a modulation codeof direct sequence spread spectrum signalling received by the module forreceiving signalling, a sequence of the synchronisation codecorresponding to a sequence of the modulation code; the reference timeis associated with the of transmission of a particular reference portionof a modulation code of the direct sequence spread spectrum signalling;and the offset time is associated with the time of transmission of asubsequently transmitted offset portion of the modulation code of thedirect sequence spread spectrum signalling.
 27. A non-transitorycomputer-readable medium, encoded with instructions that, when executedby a computer, perform the method of claim
 26. 28. A method of receivingcode phase time signalling, using at least one processor and at leastone memory comprising computer code, the at least one memory and thecomputer program code configured to, with the at least one processor,perform: receiving code phase time signalling, the code phase timesignalling representing an offset time of a synchronisation code from areference time, wherein: the reference time is associated with the timeof transmission of a particular reference portion of a modulation codeof received direct sequence spread spectrum signalling, and the offsettime is associated with the time of transmission of a subsequentlytransmitted portion of the modulation code of the direct sequence spreadspectrum signalling, and wherein a sequence of the synchronisation codecorresponds to a sequence of the modulation code; and use the code phasetime signalling to synchronize the phase of a synchronisation codeprovided from within a module for receiving signalling with the phase ofthe modulation code of the direct sequence spread spectrum signallingreceived by the module for receiving signalling, to assist in signalacquisition of direct sequence spread spectrum signalling received bythe module for receiving signalling.
 29. A non-transitorycomputer-readable medium, encoded with instructions that, when executedby a computer, perform the method of claim
 28. 30. An apparatus forproviding code phase time signalling comprising at least one processorand at least one memory comprising computer code, the at least onememory and the computer program code configured to, with the at leastone processor, cause the apparatus to: provide code phase timesignalling representing an offset time of a synchronisation code from areference time, wherein: the code phase time signalling is configured tobe used by an apparatus for receiving signalling to synchronise thephase of a synchronisation code provided from within the apparatus forreceiving signalling with the phase of a modulation code of directsequence spread spectrum signalling received by the apparatus forreceiving signalling, a sequence of the synchronisation codecorresponding to a sequence of the modulation code; the reference timeis associated with the time of transmission of a particular referenceportion of a modulation code of the direct sequence spread spectrumsignalling; and the offset time is associated with the time oftransmission of a subsequently transmitted offset portion of themodulation code of the direct sequence spread spectrum signalling. 31.An apparatus for receiving signalling, comprising at least one processorand at least one memory comprising computer code, the at least onememory and the computer program code configured to, with the at leastone processor, cause the apparatus for receiving signalling to: receivecode phase time signalling, the code phase time signalling representingan offset time of a synchronisation code from a reference time, wherein:the reference time is associated with the time of transmission of aparticular reference portion of a modulation code of received directsequence spread spectrum signalling, and the offset time is associatedwith the time of transmission of a subsequently transmitted portion ofthe modulation code of the direct sequence spread spectrum signalling,and wherein a sequence of the synchronisation code corresponds to asequence of the modulation code; and use the code phase time signallingto synchronise the phase of a synchronisation code provided from withinthe apparatus for receiving signalling with the phase of the modulationcode of the direct sequence spread spectrum signalling received by theapparatus for receiving signalling to assist in signal acquisition ofdirect sequence spread spectrum signalling received by the apparatus forreceiving signalling.
 32. A code phase time signalling providercomprising at least one processor and at least one memory comprisingcomputer code, the at least one memory and the computer program codeconfigured to, with the at least one processor, cause the code phasetime signalling provider to: provide, to an output, code phase timesignalling representing an offset time of a synchronisation code from areference time, wherein: the code phase time signalling is configured tobe used by a signalling receiver to synchronise the phase of asynchronisation code provided from within the signalling receiver withthe phase of a modulation code of the direct sequence spread spectrumsignalling received by the signalling receiver, a sequence of thesynchronisation code corresponding to a sequence of the modulation code;the reference time is associated with the time of transmission of aparticular reference portion of a modulation code of the direct sequencespread spectrum signalling; and the offset time is associated with thetime of transmission of a subsequently transmitted offset portion of themodulation code of the direct sequence spread spectrum signalling.
 33. Asignalling receiver comprising at least one processor and at least onememory comprising computer code, the at least one memory and thecomputer program code configured to, with the at least one processor,cause the signalling receiver to: receive code phase time signallingrepresenting an offset time of a synchronisation code from a referencetime, wherein: the reference time is associated with the time oftransmission of a particular reference portion of a modulation code ofreceived direct sequence spread spectrum signalling, and the offset timeis associated with the time of transmission of a subsequentlytransmitted portion of the modulation code of the direct sequence spreadspectrum signalling, and wherein a sequence of the synchronisation codecorresponds to a sequence of the modulation code; and use the code phasetime signalling to synchronise the phase of a synchronisation codeprovided from within the signalling receiver with the phase of themodulation code of the direct sequence spread spectrum signallingreceived by the signalling receiver, to assist in signal acquisition ofdirect sequence spread spectrum signalling received by the signallingreceiver.